This invention relates to an exhaust gas recirculation control method for internal combustion engines for vehicles, and more particularly to a method of this kind which is capable of improving the driveability of the engine upon starting from its standing position, particularly the accelerability, without spoiling the emission characteristics of the engine.
It has already been known and widely practiced to return part of exhaust gases emitted from an internal combustion engine for automotive vehicles to the intake passage of the engine by way of an exhaust gas recirculating passageway during operation of the engine as generally abbreviated as "EGR", so as to restrain an excessive increase in the combustion temperature of an air/fuel mixture supplied to the engine, thereby preventing occurrence of NOx causing air pollution.
While this exhaust gas recirculation is certainly an effective measure for preventing air pollution by exhaust gases, it has the disadvantage that high engine output is not obtained when the exhaust gas recirculation is carried out when the vehicle speed is low, particularly when the vehicle is accelerated from its standing state, badly affecting the accelerability of the engine. For instance, if the engine is accelerated from its idling point, it inevitably enters an operating region wherein the exhaust gas recirculation is to be effected while it is being accelerated, and simultaneously upon entering the above operating region, the exhaust gas recirculation is started. This causes a restrained rise in the combustion temperature and consequent insufficient engine output, degrading the accelerability of the engine.